Depletion of hydrocarbons and concomitant shift in bacterial community structure of a diesel-spiked tropical agricultural soil.

Bacterial community of a diesel-spiked agricultural soil was monitored over a 42-day period using the metagenomic approach in order to gain insight into key phylotypes impacted by diesel contamination and be able to predict end point of bioattenuation. Soil physico-chemical parameters showed significant differences (P < 0.05) between the Polluted Soil (PS) and the Unpolluted control (US)across time points. After 21 days, the diesel content decreased by 27.39%, and at the end of 42 days, by 57.11%. Aromatics such as benzene, anthanthrene, propylbenzene, phenanthrenequinone, anthraquinone, and phenanthridine were degraded to non-detected levels within 42 days, while some medium range alkanes and polyaromatics such as acenaphthylene, naphthalene, and anthracene showed significant levels of degradation. After 21 days (LASTD21), there was a massive enrichment of the phylum Proteobacteria (72.94%), a slight decrease in the abundance of phylum Actinobacteriota (12.74%), and > 500% decrease in the abundance of the phylum Acidobacteriodota (5.26%). Day 42 (LASTD42) saw establishment of the dominance of the Proteobacteria (34.95%), Actinobacteriota, (21.71%), and Firmicutes (32.14%), and decimation of phyla such as Gemmatimonadota, Planctomycetota, and Verrucromicrobiota which play important roles in the cycling of elements and soil health. Principal component analysis showed that in PS moisture contents, phosphorus, nitrogen, organic carbon, had greater impacts on the community structure in LASTD21, while acidity, potassium, sodium, calcium and magnesium impacted the control sample. Recovery time of the soil based on the residual hydrocarbons at Day 42 was estimated to be 229.112 d. Thus, additional biostimulation may be required to achieve cleanup within one growing season.

Functional characterization of the ABC transporters and transposable elements of an uncultured Paracoccus sp. recovered from a hydrocarbon-polluted soil metagenome.

Environmental microorganisms usually exhibit a high level of genomic plasticity and metabolic versatility that allow them to be well-adapted to diverse environmental challenges. This study used shotgun metagenomics to decipher the functional and metabolic attributes of an uncultured Paracoccus recovered from a polluted soil metagenome and determine whether the detected attributes are influenced by the nature of the polluted soil. Functional and metabolic attributes of the uncultured Paracoccus were elucidated via functional annotation of the open reading frames (ORFs) of its contig. Functional tools deployed for the analysis include KEGG, KEGG KofamKOALA, Clusters of Orthologous Groups of proteins (COG), Comprehensive Antibiotic Resistance Database (CARD), and the Antibiotic Resistance Gene-ANNOTation (ARG-ANNOT V6) for antibiotic resistance genes, TnCentral for transposable element, Transporter Classification Database (TCDB) for transporter genes, and FunRich for gene enrichment analysis. Analyses revealed the preponderance of ABC transporter genes responsible for the transport of oligosaccharides (malK, msmX, msmK, lacK, smoK, aglK, togA, thuK, treV, msiK), monosaccharides (glcV, malK, rbsC, rbsA, araG, ytfR, mglA), amino acids (thiQ, ynjD, thiZ, glnQ, gluA, gltL, peb1C, artP, aotP, bgtA, artQ, artR), and several others. Also detected are transporter genes for inorganic/organic nutrients like phosphate/phosphonate, nitrate/nitrite/cyanate, sulfate/sulfonate, bicarbonate, and heavy metals such as nickel/cobalt, molybdate/tungstate, and iron, among others. Antibiotic resistance genes that mediate efflux, inactivation, and target protection were detected, while transposable elements carrying resistance phenotypes for antibiotics and heavy metals were also annotated. The findings from this study have established the resilience, adaptability, and survivability of the uncultured Paracoccus in the hydrocarbon-polluted soil.

Isolation and characterization of biosurfactant producing bacteria from Mile 2 and Ologe Lagoons, Nigeria

Aims@#This study was aimed to isolate and characterize biosurfactant producing bacteria from Mile 2 and Ologe Lagoon which are sinks for domestic and industrial waste waters and potential source of value added bioresources such as biosurfactants, hydrocarbon degraders and organisms with potential for biotechnological applications.@*Methodology and results@#Physicochemical parameters of the two lagoon waters were analyzed using standard procedures. Bacteria were isolated using enrichment techniques on 1% Escravos light crude oil, palm oil and groundnut oil on mineral salt medium (MSM). Biosurfactant production by the isolates was assayed by hemolytic activity, oil spread test, blue agar test and emulsification activity. Isolates were identified using their colony morphologies and biochemical characteristics, while the antibiotic susceptibility of the isolates was determined using multidisc. The physicochemistry of the lagoon water showed high nitrate content of 15.7 mg/L and 19.6 mg/L for Mile 2 and Ologe Lagoon, respectively. Total hydrocarbon content (THC) of both lagoon waters was low, with values 0.53 mg/L for Mile 2 Lagoon and 0.44 mg/L for Ologe Lagoon. The predominant genera of bacteria identified include Micrococcus, Bacillus, Pseudomonas, Acinetobacter, Stomatococcus and Moraxella. A total of 23 bacterial isolates were tested for hemolytic activity, of which 13 showed β-hemolysis which is presumptive for biosurfactant production, 5 showed α-hemolysis and the remaining 5 exhibited γ-hemolysis. Majority of the isolates were positive for oil spread assay and blue agar test (19) indicating production of anionic biosurfactant. The isolates showed good emulsification activity; AGG3 (67.7%), AGG1 (62.3%), AGG2 (60%), AGG4 (60%), MTP2 (56%), AGC4 (54%) and the least emulsification value of 23.3% for strain AGP1. Most of the isolates were susceptible to ciprofloxacin, perfloxacin and showed resistance to septrin and erythromycin.@*Conclusion, significance and impact of study@#This study showed that Mile 2 and Ologe Lagoon are a potential source of biosurfactant producers with diverse emulsification properties and prospective industrial applications. This would have implication for economic empowerment, as well as sustainable and environmentally friendly clean-up technology in both locally and globally.

Impact of spent engine oil contamination on the antibiotic resistome of a tropical agricultural soil.

Profiling of hydrocarbon-contaminated soils for antibiotic resistance genes (ARGs) is becoming increasingly important due to emerging realities of their preponderance in hydrocarbon-inundated matrices. In this study, the antibiotic resistome of an agricultural soil (1S) and agricultural soil contaminated with spent engine oil (AB1) were evaluated via functional annotation of the open reading frames (ORFs) of their metagenomes using the comprehensive antibiotic database (CARD) and KEGG KofamKOALA. CARD analysis of AB1 metagenome revealed the detection of 24 AMR (antimicrobial resistance) gene families, 66 ARGs, and the preponderance (69.7%) of ARGs responsible for antibiotic efflux in AB1 metagenome. CARD analysis of 1S metagenome revealed four AMR gene families and five ARGs. Functional annotation of the two metagenomes using KofamKOALA showed 171 ARGs in AB1 and 29 ARGs in 1S, respectively. Majority of the detected ARGs in AB1 (121; 70.8%) and 1S (16; 55.2%) using KofamKOALA are responsible for antibiotic efflux while ARGs for other resistance mechanisms were also detected. All the five major antibiotic efflux pump systems were detected in AB1 metagenome, though majority of the ARGs for antibiotic efflux belong to the RND (resistance-nodulation-cell division) and MFS (major facilitator superfamily) efflux systems. Significant differences observed in the ARGs recovered from 1S and AB1 metagenomes were statistically validated (P < 0.05). SEO contamination is believed to be responsible for ARGs increase in AB1 metagenome via mechanisms of cross-resistance especially with efflux pumps. The detection of these ARGs is of great public health concern in this era of multidrug resistant isolates resurgence.

Remarkable shift in structural and functional properties of an animal charcoal-polluted soil accentuated by inorganic nutrient amendment.

BACKGROUND: Soils polluted with animal charcoal from skin and hide cottage industries harbour extremely toxic and carcinogenic hydrocarbon pollutants and thus require a bio-based eco-friendly strategy for their depuration. The effects of carbon-free mineral medium (CFMM) amendment on hydrocarbon degradation and microbial community structure and function in an animal charcoal-polluted soil was monitored for 6 weeks in field moist microcosms consisting of CFMM-treated soil (FN4) and an untreated control (FN1). Hydrocarbon degradation was monitored using gas chromatography-flame ionization detector (GC-FID), and changes in microbial community structure were monitored using Kraken, while functional annotation of putative open reading frames (ORFs) was done using KEGG KofamKOALA and NCBI's conserved domain database (CDD). RESULTS: Gas chromatographic analysis of hydrocarbon fractions revealed the removal of 84.02% and 82.38% aliphatic and 70.09% and 70.14% aromatic fractions in FN4 and FN1 microcosms in 42 days. Shotgun metagenomic analysis of the two metagenomes revealed a remarkable shift in the microbial community structure. In the FN4 metagenome, 92.97% of the population belong to the phylum Firmicutes and its dominant representative genera Anoxybacillus (64.58%), Bacillus (21.47%) and Solibacillus (2.39%). In untreated FN1 metagenome, the phyla Proteobacteria (56.12%), Actinobacteria (23.79%) and Firmicutes (11.20%), and the genera Xanthobacter (9.73%), Rhizobium (7.49%) and Corynebacterium (7.35%), were preponderant. Functional annotation of putative ORFs from the two metagenomes revealed the detection of degradation genes for aromatic hydrocarbons, benzoate, xylene, chlorocyclohexane/chlorobenzene, toluene and several others in FN1 metagenome. In the FN4 metagenome, only seven hydrocarbon degradation genes were detected. CONCLUSION: This study revealed that though CFMM amendment slightly increases the rate of hydrocarbon degradation, it negatively impacts the structural and functional properties of the animal charcoal-polluted soil. It also revealed that intrinsic bioremediation of the polluted soil could be enhanced via addition of water and aeration.

Molecular diversity, geographic distribution and host range of monocot-infecting mastreviruses in Africa and surrounding islands.

Maize streak virus (MSV), an important pathogen of maize in Africa, is the most extensively studied member of the Mastrevirus genus in the family Geminiviridae. Comparatively little is known about other monocot-infecting African mastreviruses, most of which infect uncultivated grasses. Here we determine the complete sequences of 134 full African mastrevirus genomes from predominantly uncultivated Poaceae species. Based on established taxonomic guidelines for the genus Mastrevirus, these genomes could be classified as belonging to the species Maize streak virus, Eragrostis minor streak virus, Maize streak Reunion virus, Panicum streak virus, Sugarcane streak Reunion virus and Sugarcane streak virus. Together with all other publicly available African monocot-infecting mastreviruses, the 134 new isolates extend the known geographical distributions of many of these species, including MSV which we found infecting Digitaria sp. on the island of Grand Canaria: the first definitive discovery of any African monocot-infecting mastreviruses north-west of the Saharan desert. These new isolates also extend the known host ranges of both African mastrevirus species and the strains within these. Most notable was the discovery of MSV-C isolates infecting maize which suggests that this MSV strain, which had previously only ever been found infecting uncultivated species, may be in the process of becoming adapted to this important staple crop.

Influence of pH, temperature and nutrient addition on the degradation of atrazine by Nocardioides spp. isolated from agricultural soil in Nigeria

Aims: To effectively exploit the atrazine degrading capabilities of Nocardioides spp. isolated from agricultural soil samples in Nigeria and ascertain the effect of pH, temperature and nutrient addition on the degradation process. Methodology and results: Isolates were cultivated on atrazine mineral salts medium at a temperature range of 4 °C - 45 °C and a pH range of 3-10. An optimum atrazine degrading activity was observed in the isolates between temperatures of 25 °C and 37 °C and between pH 5 and 8. Different carbon sources (glycerine, glucose, chitin, cellulose and sodium citrate) and nitrogen sources (urea, biuret, cyanuric acid, potassium nitrate and ammonium chloride) were also added to the medium. The addition of carbon and nitrogen sources did not increase degradation rates although urea and glycerine repressed the degradation ability of the isolates. Statistical analyses of variance at P < 0.05 showed no significant differences in the growth and degradation rates by both bacterial isolates under these conditions. Conclusion, significance and impact study: Atrazine degradation by Nocardioides spp. is pH and temperature dependent, and requires no additional sources of carbon and nitrogen. Hence, its use in bioremediation of atrazine contaminated agricultural soil should be explored.

Metal biouptake by actively growing cells of metal-tolerant bacterial strains.

Metal uptake potentials of Pseudomonas aeruginosa CA207Ni, Burkholderia cepacia CA96Co, Rhodococcus sp. AL03Ni, and Corynebacterium kutscheri FL108Hg were studied to determine their competence in detoxification of toxic metals during growth. Metabolism-dependent metal biouptake of the bacteria revealed appreciable uptake of the metals (57-61, 10-30, 23-60, and 10-16 mg g dw(-1) of Ni(2+), Cr(6+), Co(2+), and Cd(2+), respectively) from medium, after initial drop in pH, without lag phase. The bacteria exhibited 95-100% removal efficiency for the metals from aqueous medium as 21 (±0.8)-84 (±2.0) concentration factors of the metals were transported into the bacterial systems. Passive adsorption onto the cell surfaces occurred within 2-h contact, and afterwards, there was continuous accumulation for 12 days. Biosorption data of the bacteria were only fitted into Langmuir isotherm model when strains AL96Co, CA207Ni, and AL03Ni interacted with Ni(2+), achieving maximum uptake of 9.87, 2.72, and 2.69 mg g dw(-1), respectively. This study established that the actively growing bacterial strains displayed, at least, 97.0% (±1.5) continuous active removals of metals upon adsorption. The bacteria would be good candidates for designing bioreactor useful in the detoxification campaign of heavy metal-polluted systems.

A high degree of African streak virus diversity within Nigerian maize fields includes a new mastrevirus from Axonopus compressus.

The A-strain of maize streak virus (MSV-A; genus Mastrevirus, family Geminiviridae), the causal agent of maize streak disease, places a major constraint on maize production throughout sub-Saharan Africa. In West-African countries such as Nigeria, where maize is not cultivated year-round, this MSV strain is forced to overwinter in non-maize hosts. In order to both identify uncultivated grasses that might harbour MSV-A during the winter season and further characterise the diversity of related maize-associated streak viruses, we collected maize and grass samples displaying streak symptoms in a number of Nigerian maize fields. From these we isolated and cloned 18 full mastrevirus genomes (seven from maize and 11 from various wild grass species). Although only MSV-A isolates were obtained from maize, both MSV-A and MSV-F isolates were obtained from Digitaria ciliaris. Four non-MSV African streak viruses were also sampled, including sugarcane streak Reunion virus and Urochloa streak virus (USV) from Eleusine coacana, USV from Urochloa sp., maize streak Reunion virus (MSRV) from both Setaria barbata and Rottboellia sp., and a novel highly divergent mastrevirus from Axonopus compressus, which we have tentatively named Axonopus compressus streak virus (ACSV). Besides the discovery of this new mastrevirus species and expanding the known geographical and host ranges of MSRV, we have added D. ciliaris to the list of uncultivated species within which Nigerian MSV-A isolates are possibly able to overwinter.

Priming of Production in Maize of Volatile Organic Defence Compounds by the Natural Plant Activator cis-Jasmone.

cis-Jasmone (CJ) is a natural plant product that activates defence against herbivores in model and crop plants. In this study, we investigated whether CJ could prime defence in maize, Zea mays, against the leafhopper, Cicadulina storeyi, responsible for the transmission of maize streak virus (MSV). Priming occurs when a pre-treatment, in this case CJ, increases the potency and speed of a defence response upon subsequent attack on the plant. Here, we tested insect responses to plant volatile organic compounds (VOCs) using a Y-tube olfactometer bioassay. Our initial experiments showed that, in this system, there was no significant response of the herbivore to CJ itself and no difference in response to VOCs collected from unexposed plants compared to CJ exposed plants, both without insects. VOCs were then collected from C. storeyi-infested maize seedlings with and without CJ pre-treatment. The bioassay revealed a significant preference by this pest for VOCs from infested seedlings without the CJ pre-treatment. A timed series of VOC collections and bioassays showed that the effect was strongest in the first 22 h of insect infestation, i.e. before the insects had themselves induced a change in VOC emission. Chemical analysis showed that treatment of maize seedlings with CJ, followed by exposure to C. storeyi, led to a significant increase in emission of the defensive sesquiterpenes (E)-(1R,9S)-caryophyllene, (E)-α-bergamotene, (E)-ß-farnesene and (E)-4,8-dimethyl-1,3,7-nonatriene, known to act as herbivore repellents. The chemical analysis explains the behavioural effects observed in the olfactometer, as the CJ treatment caused plants to emit a blend of VOCs comprising more of the repellent components in the first 22 h of insect infestation than control plants. The speed and potency of VOC emission was increased by the CJ pre-treatment. This is the first indication that CJ can prime plants for enhanced production of defensive VOCs antagonist towards herbivores.

Biodegradation of petroleum hydrocarbons in the presence of nickel and cobalt.

Bioremediation of environments co-contaminated with hydrocarbons and heavy metals often pose a challenge as heavy metals exert toxicity to existing communities of hydrocarbon degraders. Multi-resistant bacterial strains were studied for ability to degrade hydrocarbons in chemically defined media amended with 5.0 mM Ni(2+), and Co(2+). The bacteria, Pseudomonas aeruginosa CA207Ni, Burkholderia cepacia AL96Co, and Corynebacterium kutscheri FL108Hg, utilized crude oil and anthracene without lag phase at specific growth rate spanning 0.3848-0.8259 per day. The bacterial populations grew in hydrocarbon media amended with nickel (Ni) and cobalt (Co) at 0.8393-1.801 days generation time (period of exponential growth, t = 15 days). The bacteria degraded 96.24-98.97, and 92.94-96.24% of crude oil, and anthracene, respectively, within 30 days without any impedance due to metal toxicity (at 5.0 mM). Rather, there was reduction of Ni and Co concentrations in the axenic culture 30 days post-inoculation to 0.08-0.12 and 0.11-0.15 mM, respectively. The metabolic functions of the bacteria are active in the presence of toxic metals (Ni and Co) while utilizing petroleum hydrocarbons for increase in biomass. These findings are useful to other baseline studies on decommissioning of sites co-contaminated with hydrocarbons and toxic metals.

Chromium (VI) biosorption properties of multiple resistant bacteria isolated from industrial sewerage.

Chromium (VI) [Cr (VI)] biosorption by four resistant autochthonous bacterial strains was investigated to determine their potential for use in sustainable marine water-pollution control. Maximum exchange between Cr (VI) ions and protons on the cells surfaces were at 30-35 °C, pH 2.0 and 350-450 mg/L. The bacterial strains effectively removed 79.0-90.5 % Cr (VI) ions from solution. Furthermore, 85.3-93.0 % of Cr (VI) ions were regenerated from the biomasses, and 83.4-91.7 % of the metal was adsorbed when the biomasses was reused. Langmuir isotherm performed better than Freundlich isotherm, depicting that Cr (VI) affinity was in the sequence Rhodococcus sp. AL03Ni > Burkholderia cepacia AL96Co > Corynebacterium kutscheri FL108Hg > Pseudomonas aeruginosa CA207Ni. Biosorption isotherms confirmed that Rhodococcus sp. AL03Ni was a better biosorbent with a maximum uptake of 107.46 mg of Cr (VI) per g (dry weight) of biomass. The results highlight the high potential of the organisms for bacteria-based detoxification of Cr (VI) via biosorption.

Reconstructing the history of maize streak virus strain a dispersal to reveal diversification hot spots and its origin in southern Africa.

Maize streak virus strain A (MSV-A), the causal agent of maize streak disease, is today one of the most serious biotic threats to African food security. Determining where MSV-A originated and how it spread transcontinentally could yield valuable insights into its historical emergence as a crop pathogen. Similarly, determining where the major extant MSV-A lineages arose could identify geographical hot spots of MSV evolution. Here, we use model-based phylogeographic analyses of 353 fully sequenced MSV-A isolates to reconstruct a plausible history of MSV-A movements over the past 150 years. We show that since the probable emergence of MSV-A in southern Africa around 1863, the virus spread transcontinentally at an average rate of 32.5 km/year (95% highest probability density interval, 15.6 to 51.6 km/year). Using distinctive patterns of nucleotide variation caused by 20 unique intra-MSV-A recombination events, we tentatively classified the MSV-A isolates into 24 easily discernible lineages. Despite many of these lineages displaying distinct geographical distributions, it is apparent that almost all have emerged within the past 4 decades from either southern or east-central Africa. Collectively, our results suggest that regular analysis of MSV-A genomes within these diversification hot spots could be used to monitor the emergence of future MSV-A lineages that could affect maize cultivation in Africa.

Behavioral responses of the leafhopper, Cicadulina storeyi China, a major vector of maize streak virus, to volatile cues from intact and leafhopper-damaged maize.

The chemical ecology of the leafhopper, Cicadulina storeyi China (Homoptera: Cicadellidae), an important vector of Maize Streak Virus (MSV), was studied with a view to developing novel leafhopper control strategies in sub-Saharan Africa. Choice tests using a Y-tube olfactometer revealed that odors from uninfested maize seedlings (Zea mays cv. Delprim) were significantly more attractive to C. storeyi than odors from C. storeyi-infested seedlings. Headspace samples of volatile organic compounds (VOCs) collected from 10 to 12 day-old uninfested seedlings were more attractive than those collected from infested seedlings. While VOCs collected from uninfested maize seedlings were attractive, VOCs collected from C. storeyi-infested seedlings were significantly repellent. Analysis of the collected VOCs by gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) led to the identification of myrcene, linalool, (E)-2-decen-1-ol, and decanal from uninfested seedlings, and (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, benzyl acetate, indole, geranyl acetate, (E)-caryophyllene, α-bergamotene, (E)-ß-farnesene, ß-sesquiphellandrene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT) from infested seedlings. Of these, methyl salicylate, (E)-caryophyllene, (E)-ß-farnesene, and TMTT were identified previously as volatile semiochemicals involved in plant defense against other sucking insect pests. When tested individually for behavioral activity, all compounds were repellent for C. storeyi. Moreover, when these induced VOCs were added to the blend of VOCs from uninfested maize seedlings, a shift from attraction to repellency was observed. Addition of methyl salicylate, (E)-ß-farnesene, or TMTT resulted in a choice for the solvent control (i.e., repulsion), whereas addition of (E)-caryophyllene resulted in no reduction in host VOC attractiveness. These results show that VOCs induced in maize have the potential to be exploited in the control of viruliferous leafhoppers in sub-Saharan Africa.

Comparative analysis of Panicum streak virus and Maize streak virus diversity, recombination patterns and phylogeography.

BACKGROUND: Panicum streak virus (PanSV; Family Geminiviridae; Genus Mastrevirus) is a close relative of Maize streak virus (MSV), the most serious viral threat to maize production in Africa. PanSV and MSV have the same leafhopper vector species, largely overlapping natural host ranges and similar geographical distributions across Africa and its associated Indian Ocean Islands. Unlike MSV, however, PanSV has no known economic relevance. RESULTS: Here we report on 16 new PanSV full genome sequences sampled throughout Africa and use these together with others in public databases to reveal that PanSV and MSV populations in general share very similar patterns of genetic exchange and geographically structured diversity. A potentially important difference between the species, however, is that the movement of MSV strains throughout Africa is apparently less constrained than that of PanSV strains. Interestingly the MSV-A strain which causes maize streak disease is apparently the most mobile of all the PanSV and MSV strains investigated. CONCLUSION: We therefore hypothesize that the generally increased mobility of MSV relative to other closely related species such as PanSV, may have been an important evolutionary step in the eventual emergence of MSV-A as a serious agricultural pathogen.The GenBank accession numbers for the sequences reported in this paper are GQ415386-GQ415401.

Recombination, decreased host specificity and increased mobility may have driven the emergence of maize streak virus as an agricultural pathogen.

Maize streak virus (MSV; family Geminiviridae, genus Mastrevirus), the causal agent of maize streak disease, ranks amongst the most serious biological threats to food security in subSaharan Africa. Although five distinct MSV strains have been currently described, only one of these - MSV-A - causes severe disease in maize. Due primarily to their not being an obvious threat to agriculture, very little is known about the 'grass-adapted' MSV strains, MSV-B, -C, -D and -E. Since comparing the genetic diversities, geographical distributions and natural host ranges of MSV-A with the other MSV strains could provide valuable information on the epidemiology, evolution and emergence of MSV-A, we carried out a phylogeographical analysis of MSVs found in uncultivated indigenous African grasses. Amongst the 83 new MSV genomes presented here, we report the discovery of six new MSV strains (MSV-F to -K). The non-random recombination breakpoint distributions detectable with these and other available mastrevirus sequences partially mirror those seen in begomoviruses, implying that the forces shaping these breakpoint patterns have been largely conserved since the earliest geminivirus ancestors. We present evidence that the ancestor of all MSV-A variants was the recombinant progeny of ancestral MSV-B and MSV-G/-F variants. While it remains unknown whether recombination influenced the emergence of MSV-A in maize, our discovery that MSV-A variants may both move between and become established in different regions of Africa with greater ease, and infect more grass species than other MSV strains, goes some way towards explaining why MSV-A is such a successful maize pathogen.

A new African streak virus species from Nigeria.

The African streak viruses (AfSVs) are a diverse group of mastrevirus species (family Geminiviridae) that infect a wide variety of annual and perennial grass species across the African continent and its nearby Indian Ocean islands. Six AfSV species (of which maize streak virus is the best known) have been described. Here we report the full genome sequences of eight isolates of a seventh AfSV species: Urochloa streak virus (USV), sampled from various locations in Nigeria. Despite there being good evidence of recombination in many other AfSV species, we found no convincing evidence that any of the USV sequences were either inter- or intra-species recombinants. The USV isolates, all of which appear to be variants of the same strain (their genome sequences are all more than 98% identical), share less than 69% nucleotide sequence identity with other currently described AfSV species.